This is a continuation-in-part of our pending application Ser. No. 305,464, filed Feb. 1, 1989, issued as U.S. Pat. No. 4,943,037 on Jul. 24, 1990, which is a continuation-in-part of our pending application Ser. No. 195,793, filed May 19, 1988, issued as U.S. Pat. No. 4,856,763 on Aug. 15, 1989.
The present invention relates to various suspension mechanisms including seat suspensions with height adjustment such as those typically used in trucks and construction and farming equipment.
There is a continuing need for suspension mechanisms that are simply constructed and inexpensive while still meeting manufacturers' ever increasing demands for compactness and comfort. An additional need exists for such a device whose suspension and ride characteristics can be easily modified.
Some seat suspensions have damping means such as shock absorbers. These suspensions have several problems. Most notably, the stroke of shock absorbers does not have a linear relationship to the vertical movement of the seat. The nonlinear relationship between the stroke of the shock absorber and the vertical movement of the seat diminishes the performance and ride characteristics of such a suspension device.
In addition, shock absorbers or other such fluid devices often have difficulty dissipating heat, especially when enclosed within a device where air circulation is not adequate. This causes both poor performance and a shorter life of the shock absorber.
Other difficulties have been encountered in the height adjustment mechanisms of seat suspensions. Frequently such mechanisms are difficult to reach, require levers or triggers that can pinch an operator, and generally are complicated and expensive. Furthermore, such mechanisms can be dangerous to operate when a vehicle is moving and the operator must grope or search for the adjustment mechanism.
Most seat suspensions are limited to a maximum of three height adjustment positions, which limits the degree of comfort that can be obtained by a driver. Some seats are difficult to adjust vertically because of the inability elevate the seat upward. At the same time, in providing a means with mechanical power to raise the seat, it is desirable to continue to avoid having difficult to reach and difficult to operate levers to actuate the power height adjustment.
Finally, most seat suspensions transmit the load from the seat to the suspension springs through steel bars comprising scissor arms or parallelogram linkages that carry virtually the entire load of the seat. These bars interact directly with the suspension springs. Thus, it has been necessary for all of those bars to be of substantial construction, thus increasing the cost and complexity of such devices. Typical of these prior art devices include the following U.S. Pat. No. 3,339,906 to Persson; U.S. Pat. No. 3,826,457 to Huot de Longchamp; and U.S. Pat. No. 4,125,242 to Meiller et al.